igneous
Weathered gray river cobble
Likely granitic or volcanic rock; exact identification is uncertain from the photograph
AI-generated identification · may be incorrectGray, rounded, and strongly weathered, with a dull granular surface and possible scattered light crystals. Likely Mohs hardness 6–7, negligible cleavage, and specific gravity about 2.6–2.8.
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Physical properties
Gray, rounded, and strongly weathered, with a dull granular surface and possible scattered light crystals. Likely Mohs hardness 6–7, negligible cleavage, and specific gravity about 2.6–2.8.
Formation & geological history
Its rounded shape indicates transport and abrasion by a stream, river, or glacial sediment; the original rock may be igneous and potentially millions to billions of years old. Surface weathering has obscured diagnostic texture.
Uses & applications
Common cobbles are used for landscaping, drainage, aggregate, and informal rock collecting; this specimen has no apparent jewelry value.
Geological facts
The image does not show enough detail to distinguish granite, basalt, gneiss, or another gray lithology confidently. A fresh broken surface, streak, magnet test, and close-up texture would improve identification.
Field identification & locations
Look for visible quartz and feldspar grains for granite, or a darker fine-grained magnetic interior for basalt. Common in streambeds, gravel deposits, glacial till, and landscaping stone.
